The Vaginal Infections and Prematurity Study is a prospective study designed to investigate the relationship between genital tract colonization with various microorganisms and the subsequent development of preterm birth. It also incorporated a clinical trial of erythromycin to prevent preterm birth among women colonized with Ureaplasma urealyticum, Chlamydia trachomatis, or group B streptococci. Currently active analyses involve the effect of erythromycin in reducing preterm birth among women colonized with group B streptococci, and the association between group B streptococcal colonization and adverse pregnancy outcome.